Nitric oxide synthesis blockade reduced the baroreflex sensitivity in trained rats

Area of Science:

• Cardiovascular Physiology
• Autonomic Nervous System Function
• Exercise Physiology

Background:

• Aerobic physical training induces significant cardiovascular autonomic adaptations.
• Nitric oxide (NO) plays a crucial role in regulating vascular tone and autonomic function.
• The interplay between NO synthesis and exercise-induced autonomic changes requires further investigation.

Purpose of the Study:

• To investigate the impact of blocking nitric oxide synthesis on cardiovascular autonomic adaptations following aerobic training.
• To assess the effects of nitric oxide blockade on systolic arterial pressure (SAP), heart rate variability (HRV), and baroreflex sensitivity in trained and untrained rats.

Main Methods:

• Male Wistar rats were divided into four groups: sedentary (SR), sedentary treated with N(omega)-nitro-l-arginine methyl ester (L-NAME) (SRL), trained (TR), and trained treated with L-NAME (TRL).
• Cardiovascular autonomic function was assessed using double blockade (methylatropine and propranolol), spectral analysis of HRV, and baroreflex sensitivity measurements.
• L-NAME was administered to inhibit nitric oxide synthesis.

Main Results:

• L-NAME treatment induced hypertension and tachycardia in sedentary rats (SRL).
• Aerobic training attenuated hypertension, but L-NAME treatment in trained rats (TRL) resulted in more pronounced bradycardia compared to trained rats (TR).
• Nitric oxide synthesis inhibition reduced baroreflex sensitivity in both sedentary and trained rats, and altered heart rate variability patterns.

Conclusions:

• Blockade of nitric oxide synthesis significantly impairs cardiovascular autonomic adaptations induced by aerobic physical training in rats.
• Decreased baroreflex sensitivity appears to be a key mechanism underlying these impairments.
• These findings highlight the critical role of nitric oxide in mediating the cardiovascular benefits of exercise.